This invention relates to systems and methods for improving the bandwidth in equalizers.
Data which is transmitted through a communications channel suffers from distortion due to the frequency-dependent transmission properties of the channel. Skin effect losses and dielectric losses are common examples of frequency-dependent channel losses which can be imposed on the signal passing through the channel. The distortion of the signal at high frequencies can lead to intersymbol interference (ISI), wherein the rising edge of a subsequent data bit is superimposed on the falling edge of the previous data bit, leading to a smearing of the transition between bits. This smearing causes increased timing jitter and reduced amplitude. The increased timing jitter makes clock recovery more difficult, whereas the reduced amplitude degrades the bit error rate performance of the channel at the output.
The frequency-dependent losses may, in theory, be compensated by applying either a precompensation to the signal at the input of the channel, or a frequency-dependent gain, or boost, to the signal at the output of the channel. Precompensation adjusts the attributes of the input signal at the transmitter to compensate for known transmission properties of the channel. However, since the transmission properties of the channel are often not known a priori, the compensation is more commonly applied to the output of the channel as receiver equalization, referred to herein as equalization.
Equalizers adjust the output signal from a channel to reverse some of the effect of distortion of the channel on the data signal. Equalizers apply a frequency-dependent amplification to the signal, such that frequencies which have been transmitted with high loss are amplified relative to frequencies which have been transmitted with low loss.